After this 0004676 bug-report has been solved we are now able to deploy JSF applications with different JSF impl version. However as these JSF applications are time consuming to start/activate its been necessary to use the lazy start-up mode:

<web-app-deploy startup-mode="lazy">

Using this mode we identified that our applications was automatically stopped/deactivated after 2 hours which is not acceptable in our environment - to overcome this we use the idle-time attribute:

<web-app-default idle-time="30D">

It seems like this attribute is the root-cause of the issue. Removing this attribute (idle-time) and removing the compiled JSP/classes from WEB-INF/work directory - forcing a recompilation, EL expressions are evaluated again.

Thus in order to reproduce this error - you must add/remove this idle-time attribute and remember to delete the compile jsp class from the work directory.